Hi Ab31,
I had the same trouble. I did exactly what you did and would go in and put dd back on her back, tuck her in and leave her to go back to sleep.
Once she did figure out how to get back down - I could hear her doing it on the baby monitor, she would cry for about ten minutes then get back down and go to sleep. But that ten minutes was quite heart wrenching and I know its not for everyone.
I guess its just a matter of waiting for her to grow out of it.
My dd goes through unsettled periods every few months, mostly when she is sick and is allowed in our bed or is given frequent breastfeed through the night. Then, once the illness has passed, we have to 'train' her back into sleeping through the night again, which for us means going in, picking her up, showing her that it is still dark outside then tucking her back into bed.
You will be pleased to know that perseverance does pay off. At 18mo, dd has now given up her bedtime breastfeed (surprisingly the first feed to be given up not the last) and goes to her bedroom door, declares 'open' and then demands to get into her cot. She then puts herself to sleep without a peep. I am amazed . However, she does still wake in the night once or twice if she is sick or teething, but goes back down quickly.
So, there is light at the end of the tunnel, it seems.
Good luck with it all - sleep deprivation is wretched.